udf: avoid redundant memcpy when writing data in ICB

Valid data within i_size in page cache will be copied to ICB cache when we
writeback the page by invoking udf_adinicb_writepage, so the copy in
udf_adinicb_write_end is redundant.

After we remove the copy, it's better to use simple_write_end directly in
udf_adinicb_aops instead of udf_adinicb_write_end.

Signed-off-by: Chao Yu <chao2.yu@samsung.com>
Signed-off-by: Jan Kara <jack@suse.cz>